The Gyarados (8 / 110) card can be found in the Holon Phantoms set.
Recently sold 3 times and based on those sales is worth around £21.17.
Currently, there are 4 open listings for this card on ebay.
This card sells in the range of £8.20 to £34.14, making it quite volatile.
This Rare Holo card was illustrated by Hajime Kusajima.